Role of Gut Microbiota on Health

It is probably hard to believe but true that well over 100 trillion microorganisms representing over 1000 different species and weighing about 1-1.5 kg reside in the human gut. These include bacteria, viruses, archaea, fungi, and protozoa. These microbes either live in a commensal relationship (meaning they live, acquire nutrients, and grow within the host without causing any harm) or in a mutualistic relationship (meaning where host and the microbes benefit from each other).

The mutualistic bacteria help the host in nutrient metabolism, synthesis of vitamins, and waste production and assist in the host’s immune system response. The Bacteroidetes, Bifidobacterium, Lactobacillus, and Prevotella are favourable microbes that help in reducing inflammation, preventing, and treating uncreative colitis and other metabolic disorders while pathogenic bacteria (Pseudomonas and Streptococcus) can be harmful to their host through the production of endo- and exo- toxins leading to diseases such as skin infections, pharyngitis, meningitis, pneumonia, and tuberculosis. are liked to skin infections, pneumonia, and sepsis.

However, both pathogenic and mutualistic microbes coexist in a healthy body without causing any harm.  But if there is a disturbance in the balance because of poor diet, prolonged use of antibiotics, or other drugs, and infectious illnesses, the body may become susceptible to these pathogenic bacteria resulting in disease.

The most common bacteria that dominate the human gut include Firmicutes (gram-positive) and Bacteroidetes (gram-negative) as well as the reasonable population of Proteobacteria, Verrumicrobia, Actinobacteria, Fusobacteria, and Cyanobacteria. Scientists believe that a diet consisting of a varied range of foods including both animal and plant-based foods can lead to the development of a diverse and healthy microbiota.  As such consumption of vegetables, legumes, grains, nuts, and seeds along with dairy and animal foods provides the environment for the development of complex ecosystems of hundreds of bacterial species, that can positively contribute to the maintenance of human health.

Further, scientific studies have revealed that individual gut microbes vary with time and are not fixed and if disturbed (because of exposure to drugs and antibiotics), their composition could change and last for a considerable time. The composition of the microbiome differs for humans who consume animal-based foods or plant-based foods. The microbiome of meat eaters tends to be rich in bile-tolerant bacteria such as Proteobacteria and Bacteroides, with the depletion of Firmicutes. Similarly, ingestion of high fat and high-sugar diet promotes the growth of Firmicutes and Proteobacteria and retards the development of Bacteroides.

 

Diet is therefore critical to the development of a healthy microbiome. Factors such as gestational age, level of sanitation, exposure to drugs and antibiotics, geography, and local food culture also contribute to the type of microbial species that colonise the gut. And as such the composition and diversity of microorganisms vary from one individual to another. The types of foods that influence the composition of gut microbiota and an individual’s health include the following:

·         Dairy products: Increase Bifidobacteria and the production of short-chain fatty acids (SCFA) that have been touted to be anti-inflammatory, immunoregulatory, anti-obesity, anti-diabetes, anticancer, hepato-, cardiovascular, and neuroprotective.  They also reduce the effect of Bacteroides and Clostridia which are associated with intestinal infections.

·         Prebiotics: These include a high-fibre diet or foods such as indigestible carbohydrates (inulin, resistant starches, gums, pectin, and fructooligosaccharides) which are only broken down in the colon by bacterial enzymes to produce SCFA. They have been found effective in stimulating immune cell activity, aiding digestion, reducing constipation, ameliorating irritable bowel disease, and possibly reducing type 2 diabetes. A balance in the consumption of a high-fibre diet is a must as it can lead to flatulence and bloating because of increased gas production.

·         Animal proteins: Promote the production of Firmicutes that are linked to atherosclerosis, obesity, inflammation, and colitis.

·         Seafood proteins: Linked with the prevention of diet-induced obesity and steatosis (accumulation of fat tissues particularly affecting the liver).

·         Dairy proteins: Increase the abundance of Lactobacillus while reducing Clostridium and are anti-obesogenic.

·         Plant polyphenols: Promotes the production of Bifidobacteria and Lactobacillus, Faecalibacterium, and reduction of E coli and Enterobacter cloacae. Increase the production of SCFA for intestinal barrier protection.

·         Artificial sweeteners: Help increase the growth of Proteobacteria and Escherichia coli, increasing faecal pH and inducing glucose intolerance.

·         Low FODMAP (Fermentable, oligosaccharides, disaccharides, monosaccharides, and polyols) diet: Increase Actinobacteria and reduce the symptoms of IBD.

·         High FODMAP: Decrease abundance of bacteria involved in gas production and reduce intestinal inflammation.

In essence, we now know that:

·         Gut microbiota greatly influences human health in particular our metabolism, digestion, immunity, and cardiovascular health among many other disorders.

·         Drugs, antibiotics, pesticides, and man-made food additives can have adverse effects on our gut microbiota.

·         Consumption of foods with high fibre content is associated with beneficial health effects.

·         Prebiotics are useful in increasing the diversity of the gut microbiota while probiotics may or may not be effective in providing the stipulated health benefits.

For more details refer to Chapter 7 of my book on Science of Food Nutrition and Health

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